Methods are known in the art for particle-particle heat exchange between granular materials and spherical metal balls of different temperatures. In one embodiment, the process is used for heating food products. The food products and metal balls are allowed to exchange heat in a rotating drum. This method allows the exchange of large quantities of heat economically and uniformly and without contamination from residues of the heat transfer medium.
Another embodiment of this process has been developed for preheating glass batch. This method employs particulate glass batch raw materials and media of larger particle size. The glass batch moves in direct and immediate physical contact with the heated media in a container. Preferably, the media is spherical. The media can be heated with an external burner or preferably heated directly or indirectly with exhaust gases from a glass melting furnace.
Durable heat transfer media formed of glass batch agglomerates, glass, ceramic, steel, stainless steel, aluminum, gravel or the like have been suggested for use in this preheating process. Alumina spheres have been found to be particularly useful. This material has shown very good results as the heat transfer media for preheating glass batch--its thermal and mechanical properties are adequate. However, as with any materials used in this manner, there will evidently be a carryover of fragments of media into the furnace by way of the preheated material. The alumina, being a refractory material, is very difficult to melt and, therefore, ends up as a stone in the finished article. This will cause serious quality problems and is unacceptable for most applications especially in glass products, e.g., container, window glass, tumblers, etc.